let me answer your queries in a chronological manner.
1. No, It is an offence. It amounts to an offence of Bigamy and you should file a criminal complaint in response to that. If proven guilty, the offender will be liable to punishment under section 494 IPC and other sections.
2. yes, it is illegal. since it amounts to an offence of cheating also and the above mentioned offence of bigamy.
3. Yes, you can file a petition under section 12 of hindu marriage act for declaring your marriage null and void and apart from that you also have an option to get divorce under section 13(1) of the hindu marriage act on the ground of cruelty. That colleague will also be a accused for bigamy and will be behind bars if proven gulity.
4. Since you have a child of 2 years you can consequently apply for guardianship of the child under section 6 of hindu minority and guardianship act. If you have the arya samaj certificate and pics of marriage then the case is strong in your favour.
You can contact me for filing the cases on your behalf.
DELHI HIGH COURT